Metal heat sinks or cooling blocks have been used extensively to improve heat dissipation from integrated circuit packages. For example, U.S. Pat. No. 3,646,409, entitled "Heat-sinking Package for Semiconductor Integrated Circuit," by van der Water et al, filed Jul. 29, 1969, issued Feb. 29, 1972, discloses a double-molded package in which a copper cooling block and, optionally, a cooling plate are provided for heat dissipation away from the lead conductors.
In providing a metal heat sink in a package, care must be taken to avoid unintended electrical short circuit forming between the heat sink and the lead frame or other electrical conductors in the package. Such short circuits are avoided by providing insulating layers, such as printed circuit board material, non-conducting resins and other insulating material. However, because an electrically insulative material is often also thermally insulative, such material preferably is provided with minimum thickness to avoid excessive loss of the ability to dissipate heat in the resulting package. For example, U.S. Pat. No. 4,916,518, entitled "Plastic Encapsulated Semiconductor Device and Method for Manufacturing the Same", Y. Yoshimura, filed Jan. 24, 1984, issued Apr. 10, 1990, discloses a heat sink formed from a mount structure of a lead frame. The mount structure is a part of the lead frame adapted for attaching an integrated circuit die. Except for one surface of the mount structure and the externals leads of the lead frames, the lead frame is encapsulated by a layer of electrically insulative resin of uniform thickness. The resin disclosed in the Yoshimura '518 patent is formed by a method which is said to provide a resin thickness (0.1-0.4 mm) thinner than Yoshimura's prior art, while minimizing pin-holes, bubbles or similar defects.
U.S. Pat. No. 4,961,106, entitled "Metal Packages having Improved Thermal Dissipation," by Butt et al., filed Aug. 31, 1987, issued Oct. 2, 1990 discloses a metallic package in which a lead frame is glass-sealed between lid and base portions, and in which the base portion comprises two parts forming a cavity therebetween filled with powder or fluid to facilitate heat dissipation.
The heat sink may also be used as a power or ground plane. For example, U.S. Pat. No. 4,975,761, entitled "High Performance Plastic Encapsulated Package for Integrated Circuit Die, " by Chu filed Sep. 5, 1989, issued Dec. 4, 1990, discloses an assembly including an insulating printed circuit board mounted on and electrically insulated from a heat sink, which may serve as a power or ground plane.
However, in the prior art, such as the structures disclosed above, numerous steps are required for assembling materials of various physical characteristics (e.g. epoxy resin, printed circuit board, powder etc.). As a result, the resulting package is expensive to manufacture, thereby increasing the cost of the integrated circuit device.